The invention is directed to a single mode optical waveguide fiber having a dispersion zero shifted to wavelengths near 1550 nm, larger effective area and low total dispersion slope. The novel waveguide fiber is a species of the genus of profiles disclosed and described in U.S. application Ser. No. 08/378,780 (abandoned).
The novel single mode waveguide design serves to maintain mode field diameter size to limit non-linear effects due to high signal power densities. In addition the novel waveguide fiber provides low attenuation and bend resistance using a simple refractive index profile design, thereby keeping manufacturing cost low. For certain of the profiles which fall within the scope of the invention, the normalized waveguide dispersion vs. wavelength curve is bimodal, thereby affording an additional characteristic which can be used in high performance telecommunications systems.
Telecommunication systems using high powered lasers, high data rate transmitters and receivers, and wavelength division multiplexing (WDM) technology require optical waveguide fiber having exceptionally low, but non-zero, total dispersion, and exceptionally low polarization mode dispersion (PMD). In addition, the waveguide fiber must have characteristics which essentially eliminate non-linear phenomena such as self phase modulation (SPM) and four wave mixing (FWM). The SPM can be limited by lowering power density. The FWM is controlled by operating in a wavelength range at which dispersion is non-zero.
A further requirement is that the optical waveguide be compatible with systems incorporating optical amplifiers.
To provide an optical waveguide having the characteristics required for these sophisticated systems, a variety of refractive index profiles have been modelled and tested. The compound core design, discussed in U.S. Pat. No. 4,715,679, Bhagavatula, offers the flexibility to meet the new system requirements while maintaining the basic requirements such as low attenuation, narrow geometry tolerances, acceptable bending resistance, and high tensile strength. Furthermore, certain of the compound core designs are relatively easy to manufacture, thereby providing enhanced optical waveguide performance without prohibitive cost increases.
A particular species of the core profile designs described in abandoned U.S. patent application Ser. No. 08/378,780 having unusual properties, has been discovered.
In telecommunications systems using wavelength division multiplexing, a preferred optical waveguide is one having a relatively flat total dispersion over the wavelength range of the multiplexed signals. For those systems which use optical amplifiers or otherwise make use of high signal power, non-linear effects such as four wave mixing and self phase modulation become system limiting factors.
Thus there is a need for an optical waveguide fiber which has a low total dispersion slope to facilitate wavelength division multiplexing, allows management of total dispersion to limit four wave mixing, and which maintains a relatively large mode field so that power per unit cross section of waveguide fiber is not too large, thereby limiting self phase modulation.
Furthermore, one wishes to maintain ease of manufacture and low manufacturing cost associated with simple refractive index profile waveguides, such as one having a step index.